1. Field of the Invention
The present invention relates to plasma treatment equipment.
2. Description of Related Art
Plasma treatment equipment shown in FIG. 12 has been known heretofore as plasma treatment equipment.
In the plasma treatment equipment, a matching circuit is provided between a high frequency power source 1 and a plasma excitation electrode 4. The matching circuit is a circuit for matching the impedance between these high frequency power source 1 and the plasma excitation electrode 4.
The high frequency power is supplied from the high frequency power source 1 to the plasma excitation electrode 4 by way of a matching circuit and through a feeder plate 3.
These matching circuit and feeder plate 3 are contained in a matching box 2 formed of a housing 21 consisting of conductive material.
A shower plate 5 having a number of holes 7 is provided under the plasma excitation electrode (cathode) 4, and a space 6 is defined by the plasma excitation electrode 4 and the shower plate 5. A gas guide pipe 17 is provided to the space 6. Gas introduced from the gas guide pipe 17 is supplied to a chamber 60 defined by a chamber wall 10 through the holes 7 of the shower plate 5. 9 denotes an insulator for insulation between the chamber wall 10 and the plasma excitation electrode (cathode) 4. An exhaust system is omitted in this drawing.
On the other hand, in the chamber 60, a wafer suscepter (suscepter electrode) 8 serves as a plasma excitation electrode having a base plate 16 placed thereon is provided, and a suscepter shield 12 is provided on the periphery of the wafer suscepter 8. The wafer suscepter 8 and suscepter shield 12 are vertically movable by means of a bellows 11 so that the distance between the plasma excitation electrodes 4 and 8 is adjustable.
The second high frequency power source 15 is connected to the wafer suscepter 8 through the matching circuit contained in a matching box 14. The DC potential of the chamber is the same as that of the suscepter shield 12.
Another conventional plasma treatment equipment is shown in FIG. 14.
The plasma treatment equipment shown in FIG. 12 is a so-called double wave excitation type plasma treatment equipment, whereas, the plasma treatment equipment shown in FIG. 14 is a single wave excitation type plasma treatment equipment. As shown in FIG. 14, the high frequency power is supplied only to the cathode 4 and the suscepter electrode 8 is grounded. Unlike the plasma treatment equipment shown in FIG. 12, there is no high frequency power source 15 and no matching box 14. The DC potential of the suscepter electrode 8 is the same as that of the chamber wall 10.
Yet another conventional plasma treatment equipment is shown in FIG. 15. There is no shower plate in the plasma treatment equipment shown in FIG. 15, and the cathode 4, which serves as a plasma excitation electrode, is disposed so as to face directly to the wafer suscepter 8. A shield 20 is provided on back side periphery of the cathode 4. This plasma treatment equipment has the same structure as that shown in FIG. 12 excepting the above-mentioned points.
Further another conventional plasma treatment equipment is shown in FIG. 16. The plasma treatment equipment shown in FIG. 15 is a so-called double wave excitation type plasma treatment equipment, whereas, the plasma treatment equipment shown in FIG. 16 is a single wave excitation type plasma treatment equipment. As shown in FIG. 16, the high frequency power is supplied only to the cathode 4, and the suscepter electrode 8 is grounded. There is no high frequency power source 15 and no matching box 14 (like that shown in FIG. 15). The DC potential of the suscepter electrode 8 is the same as that of the chamber wall 10.
However, it is found as the result of detailed study of the conventional plasma treatment equipment that the power consumption efficiency (proportion of the power consumed in plasma to the power supplied to a plasma excitation electrode 4) is not necessarily high, and particularly the power consumption efficiency decreases remarkably as the frequency supplied from a high frequency power source increases. Also it is found by the inventors of the present invention that the decrease in efficiency becomes more remarkable as the base plate size increases.
In conventional plasma treatment equipment shown in FIG. 12, FIG. 14, FIG. 15, and FIG. 16, the suscepter impedance (impedance between the suscepter and chamber) is high, and the impedance increases more as the frequency of high frequency power supplied from the high frequency power source 1 or 15 increases. In other words, the impedance depends on the frequency. As a result, the high frequency current of the plasma, which is connected to the suscepter impedance, decreases and the power consumption efficiency decreases remarkably as the frequency of high frequency power supplied from the high frequency power source 1 increases.
The power consumption efficiency is checked by a method as described herein under.
(1) The chamber wall of plasma treatment equipment is replaced with an equivalent circuit comprising a concentrated constant circuit.
(2) Constants of circuits are determined by measuring the impedance of chamber components using an impedance analyzer.
(3) The impedance of the whole chamber during discharge is measured by utilizing the relation that the impedance of the whole chamber during discharge is in complex conjugate to the impedance of the matching box provided with a 50 xcexa9 dummy load on the input side.
(4) The plasma space is regarded as a series circuit of a resistance R and capacitance C, and constants are calculated from values obtained in (2) and (3).
(5) Based on the equivalent circuit model of the chamber during discharge obtained by means of the above-mentioned method, the circuit calculation is performed and the power consumption efficiency is derived.
As described herein above, the conventional plasma treatment equipment is disadvantageous in that the film forming speed is low due to low power consumption efficiency and it is difficult to form an insulating film with high dielectric strength when a insulating film is formed.
The inventors of the present invention have studied the cause of low power consumption efficiency. As the result, the cause of the low power consumption efficiency described herein under has been found.
In detail, first, in the suscepter electrode 8 side of the conventional plasma treatment equipment shown in FIG. 12, as shown by an arrow shown in FIG. 13 which is an enlarged view of the suscepter electrode 8 shown in FIG. 12, the high frequency power is supplied from the high frequency power source 1 to a coaxial cable, the matching circuit, the feeder plate 3, and the plasma excitation electrode (cathode) 4. On the other hand, in the case that the path of the high frequency current is addressed, the current passes the plasma space (chamber 60) through these components, and the other electrode (suscepter electrode) 8, the vertical part of shield 12, the bellows 11, the bottom 10b of the chamber wall 10 and the sidewall 10s of the chamber wall 10. Then, the current passes the housing of the matching box 2 and returns to the earth of the high frequency power source 1.
In the plasma treatment equipment shown in FIG. 14, the high frequency power from the high frequency power source 1 is supplied through the coaxial cable, the matching circuit, and the feeder plate 3 and to the cathode 4. On the other hand, in the case that the path of the high frequency current is addressed, the current passes to the plasma space through these components, further to the other electrode (suscepter electrode) 8, the shaft 13, the bottom 10b of the chamber wall 10, and the side wall 10s of the chamber wall 10. Then, the current passes through the housing of the matching box 2 and returns to the earth of the high frequency power source 1.
However, in the conventional plasma treatment equipment shown in FIG. 12 and FIG. 14, the going current though the vertical part of the shield 12 and the returning current through the chamber side wall 10s are in parallel relation because the shaft 13 (or the vertical part of the shield 12 of the suscepter electrode 8) is parallel to the chamber side wall 10s, and the parallel relation results in increased mutual inductance. As the result, the power consumption efficiency is decreased, and the film forming speed is reduced or the film quality is deteriorated. The influence of the mutual inductance is larger as the base plate 16 is larger and consequently as the distance between the feeder plate 3 and the housing of the matching box 2 is larger, and particularly the influence is remarkable in the case of the base plate size of 80 to 100 cm.
Such finding associated with the above-mentioned problem was found first by the inventors of the present invention.
The present invention was accomplished to solve the above-mentioned problem and it is the object of the present invention to provides plasma treatment equipment having a small susceptance impedance with low frequency dependency and high power consumption efficiency which is capable of forming a film of excellent quality at a film forming speed higher than that of the conventional plasma treatment equipment.
Plasma treatment equipment of the present invention is characteristic in that a chamber wall and an electrode of the same DC potential as the chamber are AC shorted.
Such shorting structure allows a high frequency current to pass the shorted part where the mutual inductance with the chamber wall is smaller than the vertical part of the electrode. The mutual inductance of the high frequency current path is reduced and the consumption efficiency of the high frequency power supplied to the path is significantly improved.
It is necessary that the above-mentioned shorted part is located as near as possible to the chamber wall in order to reduce the mutual inductance effectively, the shorted part is located desirably within a length of 500 mm from the chamber wall side in horizontal direction.
Furthermore, the chamber side shorted part is located desirably within a length of 500 mm from the chamber side wall in the horizontal direction from the same view point described herein above.
In order to reduce the high frequency resistance of the path of the high frequency current through the above-mentioned shorted part to reduce the power loss by the shorted part, the above mentioned shorted part comprises a plurality of shorted parts.
Plasma treatment equipment of the present invention is characteristic in that a chamber wall and a shield of an electrode of the same DC potential as the chamber are AC shorted. The above-mentioned shorted part is desirably disposed so that the short point is located approximately at point symmetrically with respect to the center of the electrode, and thereby the path where the high frequency current flows is uniformed and plasma treatment effect is distributed uniformly on an object to be treated which is located at the center of the electrode.
The above-mentioned shorted part is desirably disposed so that the short point is located approximately at point symmetrically with respect to the center of the shield, and thereby the path where the high frequency current flows is uniformed and plasma treatment effect is distributed uniformly on an object to be treated which is located at the center of the electrode.
The present invention provides a novel impedance measurement tool. The impedance measurement tool is provided with a probe comprising a conductor, an insulating sheath coated on the conductor, and a peripheral conductor coated on the insulating sheath, and a testing tool comprising a plurality of lead wires electrically connected to the peripheral conductor of the probe and disposed radially from the center of the probe and detachable terminals provided on the free ends of the respective lead wires for detaching from the object to be measured, wherein the impedance of all series components from the probe to the detachable terminal through the lead wire are equalized each other.
By using the measurement tool having the above-mentioned structure, the impedance which will be during plasma treatment is measured correctly without restriction on the distance between two points to be measured though the object to be measured is large. A plurality of lead wires are connected to a plurality of points of an object to be measured respectively to reduce the impedance of the above-mentioned testing tool. As the result, the proportion of the impedance of an object to be measure to the impedance of the whole measurement system including the object to be measured becomes high, and the impedance is measured at higher accuracy.
The impedance measurement tool of the present invention may have the above-mentioned testing tool which is attached to the probe so as to be detachable from the probe with interposition of a probe attachment to which the other respective ends of the plurality of lead wires are electrically connected.
In the case of the structure as described herein above, various testing tools have been prepared previously, the impedance of various objects to be measured with various sizes and various configuration are measured by use of the same probe with changing a testing tool depending on the object to be measured.
The above-mentioned plurality of lead wires are desirably connected electrically to each other at the midway of the respective lead wires with another lead wire.
The number of paths of the measurement current is increased by employing the structure described herein above, and the impedance of the above-mentioned testing tool is reduced. As the result, the proportion of the impedance of an object to be measure to the impedance of the whole measurement system including the object to be measured becomes high, and the impedance is measured at higher accuracy.